Download 45.1 Inter-conversions between the functional groups

Chapter 45
Inter-conversions of carbon compounds
45.1 Inter-conversions between the functional
groups
45.2 Considerations in planning a synthetic
route
45.3 Laboratory preparation of simple carbon
compounds
P. 1 / 70
Key terms
Progress check
Summary
Concept map
P. 2 / 70
45.1 Inter-conversions between the
functional groups
Carbon compounds possessing different
functional groups usually have different physical
and chemical properties.
Example: chloroethane (CH3CH2Cl) and
ethanol (CH3CH2OH)
Same structure except the difference in functional
groups.
P. 3 / 70
Chloroethane:
gas under room conditions
slightly soluble in water
soluble in organic solvents
Ethanol:
liquid under room conditions
soluble in both water and organic solvents
45.1 Inter-conversions between the functional groups
P. 4 / 70
(a)
(b)
Figure 45.1 (a) Chloroethane is a
gas under room conditions. It is
largely used as a blowing agent in
foamed plastics. (b) Ethanol is very
soluble in water. It is dissolved in
water in alcoholic drinks.
By converting one or more functional groups to
another, we can synthesize compounds with
desired properties (e.g. solubility, melting and
boiling points, chemical reactivity, etc.).
45.1 Inter-conversions between the functional groups
P. 5 / 70
Chemists have been working hard to make new
carbon compounds that are more useful.
In organic synthesis, chemists change the
functional groups of carbon compounds.
They cannot do this without knowledge of the
inter-conversions of functional groups.
45.1 Inter-conversions between the functional groups
P. 6 / 70
Reactions of alkanes
Conversion
Example
Alkane haloalkane
CH3CH2CH2CH3
(excess) →
CH3CH2CH2CH2X
(major product)
Reactions of alkenes
Conversion
Example
Reagents and
conditions
X2 (X: Cl or Br), UV
light or heat
Reagents and
conditions
Type of
reaction
Substitution
Type of
reaction
Alkene alkane CH3CH=CH2 →
CH3CH2CH3
H2, Pt
Addition
Alkene dihaloalkane
CH3CH=CH2 →
CH3CHXCH2X
X2 (X: Cl, Br or I) in
organic solvent
Addition
Alkene haloalkane
CH3CH=CH2 →
CH3CHXCH3
(major product)
HX (X: F, Cl, Br or I)
Addition
Table 45.1 Summary of typical reactions of different functional groups.
45.1 Inter-conversions between the functional groups
P. 7 / 70
Reactions of haloalkanes
Conversion
Example
Haloalkane alcohol
CH3CH2CH2X →
CH3CH2CH2OH
(X: F, Cl, Br or I)
Reactions of alcohols
Conversion
Example
Reagents and
conditions
NaOH(aq)
Reagents and
conditions
Type of
reaction
Substitution
Type of
reaction
Alcohol haloalkane
CH3CH2CH2OH →
CH3CH2CH2X
HX or PX3
(X: Cl, Br or I)
Substitution
Alcohol alkene
CH3CH2CH2OH →
CH3CH=CH2
Conc. H2SO4, heat
or Al2O3, heat
Dehydration
1° alcohol aldehyde
CH3CH2CH2OH →
CH3CH2CHO
Cr2O72–(aq)/H+(aq), heat Oxidation
1° alcohol carboxylic acid
CH3CH2CH2OH →
CH3CH2COOH
Cr2O72–(aq)/H+(aq), heat Oxidation
2° alcohol ketone
CH3CH(OH)CH3
→ CH3COCH3
Cr2O72–(aq)/H+(aq), heat Oxidation
Table 45.1 Summary of typical reactions of different functional groups.
45.1 Inter-conversions between the functional groups
P. 8 / 70
Reactions of aldehydes and ketones
Conversion
Example
Reagents and
conditions
Type of
reaction
Aldehyde carboxylic acid
CH3CH2CHO →
CH3CH2COOH
Cr2O72–(aq)/H+(aq),
heat
Oxidation
Aldehyde 1°
alcohol
CH3CH2CHO →
CH3CH2CH2OH
1. LiAlH4, dry ether
2. H+(aq)
or NaBH4, H2O
Reduction
Ketone 2°
alcohol
CH3COCH3 →
CH3CH(OH)CH3
1. LiAlH4, dry ether
2. H+(aq)
or NaBH4, H2O
Reduction
Reactions of carboxylic acids
Conversion
Example
Reagents and
conditions
Type of
reaction
Carboxylic acid ester
CH3CH2COOH →
CH3CH2COOCH2CH3
CH3CH2OH,
conc. H2SO4, heat
Esterification
Carboxylic acid 1° alcohol
CH3CH2COOH →
CH3CH2CH2OH
1. LiAlH4, dry ether
2. H+(aq)
Reduction
Table 45.1 Summary of typical reactions of different functional groups.
45.1 Inter-conversions between the functional groups
P. 9 / 70
Carboxylic acid amide
CH3CH2COOH →
CH3CH2CONH2
1. PCl3
2. NH3
Amide
formation
Reactions of esters
Conversion
Example
Reagents and
conditions
Type of
reaction
Ester carboxylic
acid + alcohol
CH3CH2COOCH2CH3
CH3CH2COOH +
CH3CH2OH
H+(aq), heat
Acid
hydrolysis
Ester carboxylic
acid + alcohol
CH3CH2COOCH2CH3
→ CH3CH2COOH +
CH3CH2OH
1. OH–(aq), heat
2. H+(aq)
Alkaline
hydrolysis
Reactions of amides
Reagents and
conditions
Type of
reaction
Conversion
Example
Amide carboxylic
acid
CH3CH2CONH2 →
CH3CH2COOH + NH4+
H+(aq), heat
Acid
hydrolysis
Amide carboxylic
acid
CH3CH2CONH2 →
CH3CH2COOH + NH4+
1. OH–(aq), heat
2. H+(aq)
Alkaline
hydrolysis
Table 45.1 Summary of typical reactions of different functional groups.
45.1 Inter-conversions between the functional groups
P. 10 / 70
Dihaloalkanes
Amides
Esters
X2 (in
organic
solvent)
Carboxylic acids
[O], ∆
H2, Pt
Alkenes
(CnH2n)
conc. H2SO4, ∆
For 1º [O], ∆
or Al2O3, ∆ Alcohols
(ROH)
[R] or [R]
HX
Alkanes
(CnH2n+2)
Aldehydes
Ketones
X2
Haloalkanes
(RX)
UV light
or ∆
[O] – Cr2O72–(aq)/H+(aq)
[R] – 1. LiAlH4, dry ether [R] – NaBH4, water
2. H+(aq)
* ∆ = heat
Figure 45.2 Summary of methods of converting one functional group to another.
45.1 Inter-conversions between the functional groups
P. 11 / 70
Multi-step synthesis
Some functional groups can be converted to
another directly but some cannot.
Multi-step synthesis is needed.
An alkane can be converted to a haloalkane first.
Haloalkane is then allowed to react with sodium
hydroxide solution to give the required alcohol.
The synthesis involves two steps.
45.1 Inter-conversions between the functional groups
P. 12 / 70
Multi-step syntheses require more than one step,
and so one or more intermediate compounds
are produced.
Example
3 steps are required to convert compound W to
compound Z.
2 intermediate compounds (X and Y) are produced.
W
reagent
condition
X
reagent
condition
Y
reagent
condition
45.1 Inter-conversions between the functional groups
P. 13 / 70
Z
Key point
In order to convert a chosen starting material
to a target molecule, it requires a single step
or multiple steps. In either case, interconversions between functional groups are
usually needed.
45.1 Inter-conversions between the functional groups
P. 14 / 70
Inter-conversions between alkanes, alkenes,
haloalkanes and alcohols
Alkanes and alkenes are important starting
materials in organic syntheses.
Alkanes are obtained from the fractional
distillation of petroleum.
Alkenes are obtained from the cracking of
higher members of the homologous series
of alkanes.
45.1 Inter-conversions between the functional groups
P. 15 / 70
Dihaloalkanes
X2 (in
organic
solvent)
H2, Pt
Alkenes
conc. H2SO4, ∆ or
Al2O3, ∆
Alcohols
HX
Alkanes
X2
UV light
or ∆
Haloalkanes
* ∆ = heat
Figure 45.3 Inter-conversions between alkanes, alkenes, haloalkanes
and alcohols.
45.1 Inter-conversions between the functional groups
P. 16 / 70
The following route can be used to convert ethane
(an alkane) to ethanol (an alcohol).
Alcohols
Alkanes
Haloalkanes
1st step: conversion of ethane to chloroethane.
CH3–CH3
Cl2
UV light or heat
ethane
CH3–CH2–Cl
chloroethane
45.1 Inter-conversions between the functional groups
P. 17 / 70
2nd step: conversion of chloroethane (the
intermediate compound) to ethanol (the end
product).
CH3–CH2–Cl
NaOH(aq)
CH3–CH2–OH
chloroethane
ethanol
The overall process can then be represented by
the following synthetic route.
CH3–CH3
ethane
Cl2
UV light
or heat
NaOH(aq)
CH3–CH2–Cl
CH3–CH2–OH
chloroethane
ethanol
45.1 Inter-conversions between the functional groups
P. 18 / 70
Ethanol can also be converted to ethane. The
synthetic route is:
CH3–CH2–OH
ethanol
conc. H2SO4
heat
CH2=CH2
H2，Pt
ethene
CH3–CH3
ethane
In the above examples, two compounds, ethane
and ethanol, can be inter-converted by using
different reagents and conditions.
Example 45.1
Example 45.2
Class practice 45.1
45.1 Inter-conversions between the functional groups
P. 19 / 70
Inter-conversions between alcohols, aldehydes,
ketones, carboxylic acids, esters and amides
Many organic compounds find important uses as
pharmaceuticals, pesticides, perfumes and dyes.
Figure 45.4 Many synthetic dyes are
organic compounds containing
oxygen and nitrogen. They can be
used to colour fabrics.
45.1 Inter-conversions between the functional groups
P. 20 / 70
These compounds include alcohols, aldehydes,
ketones, carboxylic acids, esters and amides.
The inter-conversions between alcohols, aldehydes
and carboxylic acids are redox reactions.
Carboxylic acids can be converted to esters and
amides, and vice versa.
45.1 Inter-conversions between the functional groups
P. 21 / 70
Esters
Amides
Carboxylic
acids
[O], ∆
Alcohols
For 1º [O], ∆
Aldehydes
[R] or [R]
[O] – Cr2O72–(aq)/H+(aq)
[R] – 1. LiAlH4, dry ether
2. H+(aq)
[R] – NaBH4, water
* ∆ = heat
Ketones
Figure 45.5 Inter-conversions between alcohols, aldehydes, ketones,
carboxylic acids, esters and amides.
Concept check
45.1 Inter-conversions between the functional groups
P. 22 / 70
Alcohols are often used as the starting materials
for different oxygen-containing compounds.
Example: Convert propan-1-ol (an alcohol) to
ethyl propanoate (an ester)
Esters
Carboxylic
acids
Alcohols
Aldehydes
45.1 Inter-conversions between the functional groups
P. 23 / 70
Learning tip
A primary alcohol can be oxidized to carboxylic acid
by heating the reaction mixture under reflux.
The synthetic route is:
Cr2O72–(aq)/H+(aq)
propan-1-ol
heat
propanoic acid
CH3CH2OH, H+(aq)
heat
ethyl propanoate
Example 45.3
Class practice 45.2
45.1 Inter-conversions between the functional groups
P. 24 / 70
Inter-conversions between functional groups of
common homologous series
To convert a compound without oxygen to a
compound with oxygen, a synthetic pathway that
includes an alcohol as one of the intermediates
should be taken.
45.1 Inter-conversions between the functional groups
P. 25 / 70
Compounds without oxygen
Compounds with oxygen
Esters
Amides
Dihaloalkanes
Carboxylic
acids
X2 (in
organic
solvent)
H2, Pt
Alkenes
conc. H2SO4,
∆ or Al2O3, ∆
[O], ∆
Alcohols
For 1º [O], ∆
Aldehydes
[R] or [R]
HX
Alkanes
X2
UV light
or ∆
Ketones
Haloalkanes
[O] – Cr2O72–(aq)/H+(aq)
[R] – 1. LiAlH4, dry ether
2. H+(aq)
[R] – NaBH4, water
* ∆ = heat
Figure 45.6 Inter-conversions between alcohols and other functional groups.
45.1 Inter-conversions between the functional groups
P. 26 / 70
Example: Convert ethene (an alkene) to
ethanal (an aldehyde)
Alkenes
Alcohols
Aldehydes
Haloalkanes
45.1 Inter-conversions between the functional groups
P. 27 / 70
The synthetic route is:
NaOH(aq)
HCl
ethene
chloroethane
ethanol
distil off
2–
+
Cr2O7 (aq)/H (aq)
when
formed
ethanal
Example 45.4
Example 45.5
Class practice 45.3
45.1 Inter-conversions between the functional groups
P. 28 / 70
45.2 Considerations in planning a synthetic
route
Chemists try to synthesize the desired compounds
with the lowest costs in organic syntheses.
They would consider a number of factors in
planning a synthetic route.
1. Availability of starting materials and reagents
The starting materials and reagents of a synthetic
route should be readily available and cheap.
P. 29 / 70
2. Rate of reactions
Many organic reactions are slow.
Reactions can be speeded up by using catalysts
and a high temperature.
Lead to a higher production cost.
3. Percentage yield of the synthetic route
Organic syntheses seldom give a 100% yield
since organic reactions seldom go to completion
or by-products may be produced.
45.2 Considerations in planning a synthetic route
P. 30 / 70
Example: Direct conversion of chloroethane to
ethanol by sodium hydroxide solution
NaOH(aq)
CH3CH2Cl
CH3CH2OH
One mole (64.5 g) of chloroethane never gives
one mole (46.0 g) of ethanol.
45.2 Considerations in planning a synthetic route
P. 31 / 70
If only 23.0 g of ethanol is produced, the
percentage yield of ethanol
actual mass of ethanol obtained
× 100%
=
theoretical mass of ethanol calculated
23.0 g
× 100%
=
46.0 g
= 50%
Key point
Percentage yield of a product
actual mass of the product obtained × 100%
=
theoretical mass of the product calculated
45.2 Considerations in planning a synthetic route
P. 32 / 70
4. Number of steps in the synthetic route
If an organic synthesis consists of several steps,
the overall yield will be reduced after each step.
Example
Three-step synthesis in which each step has a
yield of 60%:
W
60%
X
60%
Y
60%
45.2 Considerations in planning a synthetic route
P. 33 / 70
Z
60 60 60
The overall yield will be
×
×
= 21 .6%
100 100 100
Therefore, a synthetic route should include as few
steps as possible.
Ethene
Ethene
Ethanol
Ethane
Chloroethane
Route (1)
Ethanol
Chloroethane
Route (2)
Figure 45.7 Possible synthetic routes for the conversion of ethene to ethanol.
45.2 Considerations in planning a synthetic route
P. 34 / 70
Ethene is converted to chloroethane in two steps
in route (1) but in three steps in route (2).
Yield of route (1) is higher than that of route (2).
5. By-products formed in the synthetic route
ethane chloroethane ethanol ......... Route (3)
ethene chloroethane ethanol ......... Route (4)
Both routes involve two steps.
45.2 Considerations in planning a synthetic route
P. 35 / 70
First step of route (3) produces not only the
desired intermediate (chloroethane), but a mixture
of haloalkane by-products such as 1,1dichloroethane, 1,2-dichloroethane, 1,1,1trichloroethane, etc.
Formation of by-products reduces the efficiency
of the synthesis.
Some of the unwanted haloalkanes may cause the
depletion of the ozone layer.
They are harmful to the environment.
Think about
45.2 Considerations in planning a synthetic route
P. 36 / 70
Hydrohalogenation of ethene in route (4)
produces only the desired intermediate
(chloroethane) which will then be converted.
The best synthetic route should produce little or
no by-products.
Harmful by-products should be avoided in organic
syntheses.
45.2 Considerations in planning a synthetic route
P. 37 / 70
Key point
In planning a synthetic route for carbon
compounds, the following factors have to be
considered:
• Availability of starting materials and
reagents
• Rate of reaction
• Percentage yield
• Number of steps
• By-products formed
Activity 45.1
STSE connections 45.1
45.2 Considerations in planning a synthetic route
P. 38 / 70
45.3 Laboratory preparation of simple
carbon compounds
Preparation of ethanoic acid
In the laboratory, ethanoic acid is usually prepared
by the oxidation of ethanol.
An acidified potassium dichromate solution
can be used as the oxidizing agent.
Ethanol is first oxidized to ethanal, and then to
ethanoic acid.
P. 39 / 70
To ensure complete oxidation of ethanol to
ethanoic acid, excess oxidizing agent is used.
The reaction mixture is heated under reflux for
20 to 30 minutes.
ethanol
loses 2
hydrogen
atoms
ethanal
gains 1
oxygen
atom
ethanoic acid
45.3 Laboratory preparation of simple carbon compounds
P. 40 / 70
Step 1: Heating the reaction mixture under reflux
Function of the reflux condenser is to condense
vapour formed from the mixture during heating.
It helps to prevent the loss of volatile organic
substances by evaporation on prolonged
heating.
45.3 Laboratory preparation of simple carbon compounds
P. 41 / 70
water out
reflux
condenser
hot vapour
condenses on
the cold inner
wall of the
condenser
water in
reflux
condenser
pearshaped
flask
water out
water in
water bath
anticondensed
liquid returns to bumping
granule
the flask
ethanol + acidified
potassium
dichromate solution
pear-shaped flask
anti-bumping
granule
water bath
ethanol +
acidified
potassium
dichromate
solution
heat
Figure 45.8 Oxidizing ethanol to ethanoic acid by heating under reflux.
45.3 Laboratory preparation of simple carbon compounds
P. 42 / 70
Ethanol is first oxidized to ethanal.
The ethanal vaporizes and condenses in the
reflux condenser.
The liquid drops back into the reaction flask and is
then further oxidized to ethanoic acid.
45.3 Laboratory preparation of simple carbon compounds
P. 43 / 70
Step 2: Distilling the product mixture
thermometer
water out
(to sink)
thermometer
pear-shaped
flask
Liebig
condenser
pear-shaped
flask
anti-bumping
granule
product
mixture
heat
product
mixture
receiver
adaptor
water in
(from tap)
Liebig
condenser
receiver
adaptor
water
out
anti-bumping
granule
test tube
(as receiver)
water
in
aqueous solution
of ethanoic acid
aqueous solution
of ethanoic acid
Figure 45.9 Distilling ethanoic acid from the product mixture.
45.3 Laboratory preparation of simple carbon compounds
P. 44 / 70
Distil the product mixture and collect the liquid
that boils between 110°C and 114°C.
The distillate obtained is an aqueous solution of
ethanoic acid and it has a strong smell of vinegar.
To obtain pure ethanoic acid, the aqueous solution
of ethanoic acid is redistilled.
The liquid that boils between 116°C and 118°C is
collected as distillate.
45.3 Laboratory preparation of simple carbon compounds
P. 45 / 70
The percentage yield of ethanoic acid can be
calculated from the amount of ethanoic acid
obtained.
Percentage yield of ethanoic acid
actual mass of ethanoic acid obtained
=
theoretical mass of ethanoic acid calculated
Example 45.6
Experiment 45.1
× 100%
Experiment 45.1
45.3 Laboratory preparation of simple carbon compounds
P. 46 / 70
Preparation of ethyl ethanoate
In the laboratory, ethyl ethanoate is prepared by
heating a mixture of ethanoic acid and ethanol in
the presence of an acid catalyst.
The process is known as esterification.
H+(aq)
ethanoic acid
ethanol
heat
ethyl ethanoate
45.3 Laboratory preparation of simple carbon compounds
P. 47 / 70
water
Learning tip
Concentrated sulphuric acid has two functions in the
laboratory preparation of ethyl ethanoate:
1. It acts as a catalyst.
2. It removes water, shifting the equilibrium of
esterification to the product side.
Esterification is a reversible reaction.
45.3 Laboratory preparation of simple carbon compounds
P. 48 / 70
Step 1: Heating the reaction mixture under reflux
Equal volumes of ethanoic acid and ethanol are
mixed and concentrated sulphuric acid is added
to the mixture.
The mixture is then heated under reflux.
SBA note
Addition of concentrated sulphuric acid to the mixture
of ethanol and ethanoic acid is highly exothermic.
Hence, the acid should be added to the mixture slowly
with cooling (in an ice-water bath) and shaking.
45.3 Laboratory preparation of simple carbon compounds
P. 49 / 70
water out
reflux
condenser
hot vapour
condenses on the
cold inner wall of
the condenser
condensed liquid
returns to the
flask
water in
pear-shaped
flask
a mixture of
ethanol, ethanoic
acid and conc.
H2SO4
anti-bumping
granule
reflux
condenser
water out
water in
pear-shaped
flask
anti-bumping
granule
heat
Figure 45.10 Heating a mixture of ethanol, ethanoic acid and
concentrated sulphuric acid under reflux.
45.3 Laboratory preparation of simple carbon compounds
P. 50 / 70
a mixture of
ethanol,
ethanoic acid
and conc.
H2SO4
Step 2: Distilling the product mixture
To separate the organic compounds (i.e. unreacted
ethanol, unreacted ethanoic acid and the product
ethyl ethanoate) from the aqueous solution, twothirds of the product mixture is distilled off.
This distillate should have a much lower percentage
of water and relatively higher percentages of
ethanol, ethanoic acid and ethyl ethanoate.
45.3 Laboratory preparation of simple carbon compounds
P. 51 / 70
thermometer
thermometer
water out
(to sink)
Liebig
condenser
pearshaped
flask
product
anti-bumping
mixture
granule
water in
heat
(from tap)
Liebig
condenser
pear-shaped
flask
receiver
adaptor
product
mixture
receiver
adaptor
water
out
anti-bumping
granule
water
in
test tube
(as receiver)
solution
of organic
compounds
Figure 45.11 Distilling off two-thirds of the reaction mixture in order to
separate the carbon compounds from the aqueous solution of the product
mixture.
45.3 Laboratory preparation of simple carbon compounds
P. 52 / 70
Step 3: Removing unreacted ethanoic acid and traces
of sulphuric acid from the distillate
The distillate is mixed with excess sodium
carbonate solution.
Sodium carbonate reacts and removes any acidic
substances (unreacted ethanoic acid and traces of
sulphuric acid) in the distillate.
The lower aqueous layer is discarded.
45.3 Laboratory preparation of simple carbon compounds
P. 53 / 70
2CH3COOH(aq) + CO32–(aq) → 2CH3COO–(aq) + H2O(l) + CO2(g)
2H+(aq) + CO32–(aq) → H2O(l) + CO2(g)
excess sodium
carbonate solution
filter funnel
organic layer
aqueous layer
separating
funnel
distillate obtained
in step 2
beaker
(b)
(a)
Figure 45.12 (a) Adding excess sodium carbonate solution removes
unreacted ethanoic acid and traces of sulphuric acid in the distillate.
(b) Discarding the aqueous layer.
45.3 Laboratory preparation of simple carbon compounds
P. 54 / 70
Step 4: Removing unreacted ethanol from the distillate
The organic layer is then mixed with excess
calcium chloride solution.
Calcium chloride reacts and removes any
unreacted ethanol in the organic layer.
An aqueous layer forms and is discarded.
45.3 Laboratory preparation of simple carbon compounds
P. 55 / 70
CaCl2(aq) + 4CH3CH2OH(l) → CaCl2․4CH3CH2OH(aq)
excess calcium
chloride solution
filter funnel
organic layer
aqueous layer
separating
funnel
organic layer
beaker
(b)
(a)
Figure 45.13 (a) Adding excess calcium chloride solution removes
unreacted ethanol in the organic layer. (b) Discarding the aqueous layer.
45.3 Laboratory preparation of simple carbon compounds
P. 56 / 70
Step 5: Removing traces of water from the distillate
Add a few lumps of anhydrous calcium chloride
to the organic layer.
The anhydrous calcium chloride is a drying agent
that removes remaining traces of water from the
organic layer.
Filter the organic layer and obtain the filtrate.
45.3 Laboratory preparation of simple carbon compounds
P. 57 / 70
separating funnel anhydrous
calcium
chloride
spatula
organic
layer
conical flask
(a)
(b)
organic
layer
Figure 45.14 (a) Pouring the organic layer to a conical flask. (b) Adding
anhydrous calcium chloride removes traces of water in the organic layer.
45.3 Laboratory preparation of simple carbon compounds
P. 58 / 70
glass rod
fluted filter paper
residue
filter funnel
pear-shaped flask Figure 45.15 Filtering the organic
filtrate
layer into a pear-shaped flask to
obtain filtrate for further distillation.
45.3 Laboratory preparation of simple carbon compounds
P. 59 / 70
Step 6: Re-distillation to obtain a second distillate
(pure ethyl ethanoate)
The filtrate obtained is then redistilled and the
liquid that boils between 74°C and 79°C is collected
as distillate.
The distillate is ethyl ethanoate.
Class practice 45.4
Experiment 45.2
Experiment 45.2
45.3 Laboratory preparation of simple carbon compounds
P. 60 / 70
Key terms
1.
2.
3.
4.
5.
6.
7.
inter-conversion 互換
intermediate compound 中間化合物
multi-step synthesis 多步驟合成
organic synthesis 有機合成
percentage yield 百分產率
reflux condenser 回流冷凝器
synthetic route 合成路線
P. 61 / 70
Progress check
1. What is the importance of inter-conversions
between functional groups in organic compounds?
2. What is a multi-step synthesis?
3. What reagents and conditions are needed for the
inter-conversions between alkanes, alkenes,
haloalkanes and alcohols?
4. What reagents and conditions are needed for the
inter-conversions between alcohols, aldehydes,
carboxylic acids, esters and amides?
P. 62 / 70
5. What is the role of alcohols for the interconversions between compounds with oxygen
and compounds without oxygen?
6. What are the essential features of a good
synthetic route?
7. What is the percentage yield of a product in a
synthetic process?
8. What are the steps in the laboratory preparation
of ethanoic acid?
9. What are the steps in the laboratory preparation
of ethyl ethanoate?
Progress check
P. 63 / 70
Summary
45.1 Inter-conversions between the functional
groups
1.
2.
3.
Some common reactions that can bring about a
change in functional groups are summarized
inFigure 45.2 on p.6.
Multi-step synthesis is the process of converting
a readily available compound into the desired
product in more than one step.
The inter-conversions between alkanes, alkenes,
haloalkanes and alcohols are summarized in
Figure 45.3 on p.7.
P. 64 / 70
4.
5.
The inter-conversions between alcohols,
aldehydes, ketones, carboxylic acids, esters and
amides in Figure 45.5 on p.11.
We can divide carbon compounds into two main
groups: one with oxygen and one without. If we
want to convert a compound without oxygen to a
compound with oxygen, a synthetic pathway that
includes an alcohol as one of the intermediates
should be taken. Refer to Figure 45.6 on p.13
Summary
P. 65 / 70
45.2 Considerations in planning a synthetic
route
6. Percentage yield of a product
actual mass of the product obtained
× 100%
=
theoretical mass of the product calculated
7.
In planning a synthetic route for carbon
compounds, the following factors have to be
considered:
- Availability of starting materials and reagents
- Rate of reaction
Summary
P. 66 / 70
- Percentage yield
- Number of steps
- By-products formed
45.3 Laboratory preparation of simple carbon
compounds
8.
In the laboratory, ethanoic acid is usually
prepared by heating ethanol under reflux with
acidified potassium dichromate solution.
Ethanoic acid is collected in the distillate by
distillation of the product mixture. It is then
purified by redistillation.
Summary
P. 67 / 70
9.
In the laboratory, ethyl ethanoate is prepared by
heating a mixture of ethanoic acid and ethanol
under reflux in the presence of an acid catalyst.
Ethyl ethanoate is collected in the distillate by
distillation of the product mixture. Unreacted
ethanol, ethanoic acid and water are removed
from the distillate. Ethyl ethanoate is then purified
by redistillation.
Summary
P. 68 / 70
Concept map
HX or PX3
Dihaloalkanes
NaOH(aq)
Alkanes
H2, Pt
X2 (in
organic
solvent) conc.
H2SO4 or
Al2O3,
Alkenes
∆
Alcohols
HX
X2, UV
light or ∆
HX or PX3
Haloalkanes
NaOH(aq)
P. 69 / 70
Esters
R’OH, H+(aq), ∆
(For 1°) Cr2O72–(aq)/H+(aq), ∆
(1) LiAlH4, dry ether
(2) H+(aq)
Carboxylic
acids
(For 1°)
Cr2O72–(aq)/H+(aq), ∆
Alcohols
H+(aq), ∆ or 1. OH–(aq), ∆
2. H+(aq)
1. PCl3
2. NH3
H+(aq), ∆
or 1. OH–(aq), ∆
Cr2O72–(aq)/
2. H+(aq)
H+(aq), ∆
Aldehydes
(1) LiAlH4, dry ether
(2) H+(aq)
or NaBH4, H2O
(For 2°)
Cr2O72–(aq)/H+(aq), ∆
Ketones
(1) LiAlH4, dry ether
(2) H+(aq)
or NaBH4, H2O
Concept map
P. 70 / 70
Amides